Lithium-ion batteries are being quickly accepted as reliable high density power storage devices, and motor vehicles, for example, may be powered at least in part by such a power storage device. In order to meet an amount of power required to run a motor vehicle, a plurality of lithium-ion batteries may be assembled into a battery pack. As such, the power storage device (e.g., battery pack) may be comprised of more than one battery cell and each battery cell may have different charging characteristics. Because battery cells may charge and discharge differently, it may be desirable to monitor individual battery cells of a battery pack. By monitoring individual battery cells, it may be possible to reduce battery cell degradation. For example, if a battery cell charge is determined to be greater than a desired level, the battery cell charge may be reduced by coupling the battery cell to a load resistor. Thus, the possibility of battery pack degradation may be reduced by monitoring battery cell charge.
However, battery cell monitoring may require circuitry, and it may be desirable to periodically assess whether or not the monitor circuitry is operating as desired. One technique for assessing whether or not battery cell monitoring circuits are operating as desired includes lowering a voltage detection threshold. As an example, the threshold voltage of voltage detection circuit may be temporarily lowered, thereby causing a voltage detector circuit to signal that the threshold voltage has been exceeded by a battery cell. Such an assessment, however, may not accurately indicate that the voltage detector is not degraded. For example, because the threshold voltage is lowered during the assessment, it is unknown if the voltage detector will indicate an exceeded threshold at the desired level (e.g., if the voltage detector threshold is lowered to 0.25 volts it is unknown whether or not the voltage detector will operate at a voltage of 1.25 volts).
Thus, the inventors herein have developed a system for assessing voltage detection circuitry within a battery pack. In particular, the inventors have developed a system for assessing voltage threshold detection circuitry of individual battery cells within a battery pack supplying power to a vehicle, comprising: a plurality of battery cells within a battery pack, a plurality of voltage threshold detecting circuits detecting voltage of the plurality of battery cells, a voltage of a first battery cell of the plurality of battery cells coupled to a first voltage threshold detecting circuit of the plurality of voltage threshold detecting circuits, and a network that selectively couples a second battery cell to said first voltage detecting circuit while the first battery cell is coupled to the first voltage detecting circuit.
By selectively coupling the second battery cell to the first voltage detecting circuit while the first battery cell is coupled to the first voltage detecting circuit, the total voltage detected by the voltage threshold detecting circuit may be increased. Further, the system may include a plurality of networks to increase the voltage detected by the plurality of voltage detecting circuits in a similar manner. As such, the desired threshold voltage may be exceeded without decreasing the threshold that triggers voltage detection circuitry. As a result, operation of voltage detection circuitry can be assessed at a voltage level that is more representative of a voltage level that is greater than a desired threshold voltage level. Therefore, the present system may indicate degradation of voltage threshold detecting circuitry more accurately.
The present description may provide several advantages. In particular, the approach may provide an improved estimate of degradation of voltage threshold detecting circuitry for individual battery cells within a battery pack. In addition, the approach may provide improved control over the state of charge of a battery pack by increasing the possibility that battery cells will be drained of a portion of their charge when the battery voltage exceeds a threshold. Further, the approach may be more reliable than other methods.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.